Self-service terminal

A self-service terminal comprising a plurality of components associated with a valuable media, such as a card reader or cash dispenser. Each component includes or is associated with one or more sensors for detecting potentially fraudulent activity and a component agent for generating a warning signal in the event that such activity is detected. Also provided is a higher level agent that is operable to receive warning signals from the component agents, and use the received signals to identify potentially fraudulent activity. By providing a hierarchy of fraud detection agents, the likelihood of a fraud being successfully detected is improved.